System information transmission method and apparatus

ABSTRACT

When cell system information changes, a first terminal device receives, during on duration of the first terminal device, system information sent by a second terminal device, so that the first terminal device can receive the system information through a sidelink between the first terminal device and the second terminal device without a need to maintain a cellular link, thereby reducing complexity and power consumption of system information transmission. Alternatively, when cell system information changes and a first terminal device has only one receive radio frequency chain, the first terminal device obtains system information within a gap period of communication between the second terminal device and the first terminal device through a link between the first terminal device and a network device, so that the first terminal device maintains a cellular link only within the gap period, thereby reducing complexity and power consumption of system information transmission to some extent.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/496,494, filed on Sep. 23, 2019, which is a national stage ofInternational Application No. PCT/CN2017/078157, filed on Mar. 24, 2017,which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

This application relates to the field of communications technologies,and in particular, to a system information transmission method andapparatus.

BACKGROUND

A device-to-device (Device-to-Device, D2D) communication mode is acommunication mode in which a transmit end directly sends data to areceive end without forwarding by a base station or a cellular network.A relatively special mode in the D2D communication mode is aUE-to-network relay scenario. In the UE-to-network relay scenario, aterminal device (for example, user equipment (User Equipment, UE)) isconnected to a network by using another terminal device having a relayfunction. Usually, the former is referred to as a remote terminal device(Remote UE), and the latter is referred to as a relay terminal device(Relay UE).

In the UE-to-network relay scenario, if system information of acamped-on cell or a serving cell of the remote terminal device changes,a base station of the camped-on cell or the serving cell of the remoteterminal device sends a paging message to the remote terminal device,and indicates, by using the paging message, that the system informationchanges. After receiving the paging message sent by the base station,the remote terminal device determines that the system informationchanges and obtains changed system information. The remote terminaldevice needs to be located in coverage of a cell to obtain the changedsystem information, and receives the changed system information througha cellular link between the remote terminal device and the base station.

The remote terminal device receives the system information in theforegoing manner, resulting in relatively high complexity and relativelyhigh power consumption.

SUMMARY

Embodiments of this application provide a system informationtransmission method and apparatus, to reduce complexity and powerconsumption of receiving system information by a remote terminal device.

According to a first aspect, a system information transmission method isprovided. In the method, a second terminal device sends systeminformation to a first terminal device during on duration of the firstterminal device, and the first terminal device receives, during the onduration of the first terminal device, the system information sent bythe second terminal device, so that the first terminal device canreceive the system information through a sidelink between the firstterminal device and the second terminal device without a need tomaintain a cellular link, thereby reducing complexity and powerconsumption of system information transmission.

In a possible implementation, the on duration of the first terminaldevice may be a paging occasion of the first terminal device. The secondterminal device sends the system information to the first terminaldevice on the paging occasion of the first terminal device, and thefirst terminal device receives, on the paging occasion of the firstterminal device, the system information sent by the second terminaldevice, so that the first terminal can receive, regardless of whetherthe first terminal is in an RRC idle mode or an RRC connected mode, thesystem information sent by the second terminal device.

In a possible implementation, the second terminal device may use aresource in a sending resource pool that is configured or preconfiguredby a base station by using a broadcast message as a resource that isused by the second terminal device to send the system information to thefirst terminal device. The resource in the sending resource pool may bea resource that is used by the second terminal device to send a pagingmessage. The second terminal device may directly send the systeminformation by using a resource that is used by a paging messageoriginally sent by the second terminal device, and use the resource usedby the original paging message as the resource in the sending resourcepool. The second terminal device may alternatively add the systeminformation to the original paging message to obtain a new pagingmessage, and use a resource used by the new paging message as theresource in the sending resource pool. The resource in the sendingresource pool may be alternatively a resource that is specially used bythe second terminal device to send the system information to the firstterminal device.

The second terminal device sends the system information to the firstterminal device at least one time on the paging occasion of the firstterminal device by using the resource in the sending resource pool, andthe first terminal device receives, on the paging occasion of the firstterminal device, the system information sent by the second terminaldevice at least one time by using the resource in the sending resourcepool. The sending resource pool is configured or preconfigured by anetwork device by using a broadcast message.

In another possible implementation, the second terminal device mayconfigure a dedicated resource, and use the dedicated resource as aresource that is used by the second terminal device to send the systeminformation to the first terminal device. The dedicated resource isdetermined by a network device based on a dedicated resource requestedby the second terminal device from the network device and a time domainresource location that is of the paging occasion and that is indicatedby the second terminal device to the network device.

The second terminal device sends the system information to the firstterminal device at least one time on the paging occasion of the firstterminal device by using the dedicated resource, and the first terminaldevice receives, on the paging occasion of the first terminal device,the system information sent by the second terminal device at least onetime by using the dedicated resource. The dedicated resource isconfigured by the network device for the second terminal device.

In still another possible implementation, that the second terminaldevice sends the system information at least one time on the pagingoccasion of the first terminal device by using the resource in thesending resource pool or by using the dedicated resource means that thesecond terminal device sends the system information on one or morepaging occasions of the first terminal device. An implementation mayinclude: sending, by the second terminal device, the system informationon the one or more paging occasions of the first terminal device in abroadcast manner, or sending, by the second terminal device, the systeminformation on the one or more paging occasions of the first terminaldevice in a multicast manner, or sending, by the second terminal device,the system information on the one or more paging occasions of the firstterminal device in a unicast manner.

In still another possible implementation, the system information sent bythe second terminal device to the first terminal device may be systeminformation required by the first terminal device, and the systeminformation required by the first terminal device is a part or all ofsystem information delivered by a network device of a camped-on cell ora serving cell of the second terminal device.

The system information required by the first terminal device includeschanged system information in the system information required by thefirst terminal device or all system information required by the firstterminal device, and therefore the second terminal device does not needto send all the system information to the first terminal device, andsends only the changed system information to the first terminal device,thereby reducing signaling overheads of sending system informationbetween the first terminal device and the second terminal device.

The second terminal device may obtain the changed system information inone of the following manners: The network device indicates the changedsystem information in a paging message, and the second terminal devicemay determine the changed system information by receiving a pagingmessage sent by the network device. The network device indicates thechanged system information in a SIB1 message, and the second terminaldevice may determine the changed system information by receiving a SIB1message sent by the network device. The second terminal device receivessystem information sent by the network device, and compares the newlyreceived system information with currently stored original systeminformation, to further determine the changed system information.

In still another possible implementation, the second terminal device maysend indication information to the first terminal device, where theindication information is used to indicate that the system informationchanges. When determining that the system information changes, the firstterminal device receives the system information sent by the secondterminal device, so that the first terminal device receives the systeminformation only when the first terminal device needs to receive thesystem information, thereby reducing signaling overheads.

In still another possible implementation, the on duration of the firstterminal may be a time in which the second terminal device sends adiscovery message, and the system information is carried in thediscovery message sent by the second terminal device.

The system information may be carried in a reserved bit in an existingdiscovery message, or the system information may be carried in adiscovery message that is specially used for carrying the systeminformation. A bit in the discovery message that is specially used forcarrying the system information may carry the system information, andcarry some necessary information such as a destination address.

The second terminal sends, to the first terminal device, the discoverymessage that carries the system information, and the first terminal mayobtain the system information by receiving the discovery message sent bythe second terminal device, so that the first terminal device canreceive the system information through a sidelink between the firstterminal device and the second terminal device without a need tomaintain a cellular link, thereby reducing complexity and powerconsumption of system information transmission.

In still another possible implementation, the on duration of the firstterminal device may be a time in which the device is in an RRC connectedmode and may receive a message sent by the second terminal device. Thetime in which the device may receive the message sent by the secondterminal device may be understood as a time in which the first terminaldevice monitors a sidelink, and the monitoring a sidelink may bemonitoring a physical sidelink control channel (Physical SidelinkControl Channel, PSCCH), a physical sidelink shared channel (PhysicalSidelink Shared CHannel, PSSCH), a physical sidelink discovery channel(Physical Sidelink Discovery CHannel, PSDCH), a physical sidelinkbroadcast channel (Physical Sidelink Broadcast CHannel, PSBCH), or thelike. The network device determines that the system information changes,adds the system information required by the first terminal device to anRRC message, and forwards the RRC message to the second terminal device.The RRC information that carries the system information required by thefirst terminal device may be an RRC dedicated message. Further, the RRCdedicated message that carries the system information required by thefirst terminal device may be an RRC reconfiguration message.

To reduce signaling overheads of requesting a resource and allocating aresource by the second terminal device, when or after sending, to thesecond terminal device, the RRC message that carries the systeminformation required by the first terminal device, the network devicemay configure a resource that is used to forward the RRC message.

The second terminal device forwards, to the first terminal device, theRRC message that is sent by the network device and that carries thesystem information, and the first terminal obtains the systeminformation by receiving the RRC message forwarded by the secondterminal device, so that the first terminal device can receive thesystem information through a sidelink between the first terminal deviceand the second terminal device without a need to maintain a cellularlink, thereby reducing complexity and power consumption of systeminformation transmission. In addition, in the solution in which thesystem information is carried in the RRC message, regardless of whetherthe first terminal device is in coverage of a cell or is out of coverageof a cell, the first terminal device can obtain the system informationas long as the first terminal device is in an RRC connected mode. Animplementation process is simple, and an existing standard protocol isslightly changed, thereby reducing signaling overheads and resourcewaste.

According to a second aspect, a system information transmission methodis provided. A second terminal device determines that system informationrequired by a first terminal device changes; the second terminal devicesends, to the first terminal device, indication information that is usedto indicate that the system information changes; and the first terminaldevice receives the indication information sent by the second terminaldevice, and obtains the system information according to the indicationinformation.

In a possible implementation, the first terminal device may receive thesystem information through a sidelink between the first terminal deviceand the second terminal device.

In another possible implementation, if the first terminal device hasonly one receive radio frequency chain, the first terminal device mayobtain the system information within a gap period of communicationbetween the second terminal device and the first terminal device througha link between the first terminal device and a network device.Communication between the second terminal device and the first terminaldevice is suspended within the gap period. The second terminal deviceand the first terminal device may still communicate with each otherthrough a sidelink outside the gap period.

In a possible implementation, if the first terminal device is in an RRCidle mode, the gap period may be configured by the first terminal deviceor may be configured or preconfigured by the second terminal device.

If the first terminal device is in an RRC idle mode, the gap period isany time period in a sleep time of the first terminal device.

In another possible implementation, if the first terminal device is inan RRC connected mode, the gap period may be configured by the secondterminal device or the network device for the first terminal device. Thegap period configured by the second terminal device or the networkdevice for the first terminal device may be one or more modificationperiods, or may be periods of some system information windows, or may bea periodically repeated time period, or may be another customized timeperiod.

In still another possible implementation, in addition to sending, to thefirst terminal device, the indication information that is used toindicate that the system information changes, the second terminal devicemay indicate the changed system information to the first terminal, forexample, adding the changed system information to a paging message or aSIB1 message, so that the first terminal device needs to receive onlythe system information required by the first terminal device, and doesnot need to receive all system information, thereby reducing signalingoverheads. The second terminal device may indicate a type of the changedsystem information by using the indication information, so that thefirst terminal device receives system information of this type.

In still another possible implementation, to enable the first terminaldevice to accurately and quickly switch to a cellular link to obtain thesystem information, before the first terminal device obtains the systeminformation through the link between the first terminal device and thenetwork device, the first terminal device may obtain a cell identifierof a cell in which the second terminal device is located.

According to a third aspect, a system information transmission apparatusis provided. The system information transmission apparatus can implementa function of the first terminal in the method design in the firstaspect. The function may be implemented by hardware, or may beimplemented by hardware executing corresponding software. The hardwareor the software includes one or more modules corresponding to theforegoing function. The module may be software and/or hardware.

In a possible design, the first terminal device includes a processingunit and a receiving unit, and functions of the processing unit and thereceiving unit may be corresponding to the method steps. Details are notdescribed herein again.

In another possible design, the first terminal device includes aprocessor, a memory, and a receiver, and the processor, the memory, andthe receiver may be connected to each other through a bus system. Thememory is configured to store a program, and the processor is configuredto execute the program in the memory, to perform the method performed bythe first terminal device in the first aspect or any possible design ofthe first aspect.

According to a fourth aspect, a system information transmissionapparatus is provided. The system information transmission apparatus canimplement a function of the first terminal in the method design in thesecond aspect. The function may be implemented by hardware, or may beimplemented by hardware executing corresponding software. The hardwareor the software includes one or more modules corresponding to theforegoing function. The module may be software and/or hardware.

In a possible design, the first terminal device includes a receivingunit and a processing unit, and functions of the receiving unit and theprocessing unit may be corresponding to the method steps. Details arenot described herein again.

In another possible design, the first terminal device includes aprocessor, a memory, and a receiver, and the processor, the memory, andthe receiver may be connected to each other through a bus system. Thememory is configured to store a program, and the processor is configuredto execute the program in the memory, to perform the method performed bythe first terminal device in the second aspect or any possible design ofthe second aspect.

According to a fifth aspect, a system information transmission apparatusis provided. The system information transmission apparatus can implementa function of the second terminal in the method design in the firstaspect. The function may be implemented by hardware, or may beimplemented by hardware executing corresponding software. The hardwareor the software includes one or more modules corresponding to theforegoing function. The module may be software and/or hardware.

In a possible design, the second terminal device includes a processingunit and a sending unit, and functions of the processing unit and thesending unit may be corresponding to the method steps. Details are notdescribed herein again.

In another possible design, the second terminal device includes aprocessor, a memory, and a transmitter, and the processor, the memory,and the transmitter may be connected to each other through a bus system.The memory is configured to store a program, and the processor isconfigured to execute the program in the memory, to perform the methodperformed by the second terminal device in the first aspect or anypossible design of the first aspect.

According to a fourth aspect, a system information transmissionapparatus is provided. The system information transmission apparatus canimplement a function of the second terminal in the method design in thesecond aspect. The function may be implemented by hardware, or may beimplemented by hardware executing corresponding software. The hardwareor the software includes one or more modules corresponding to theforegoing function. The module may be software and/or hardware.

In a possible design, the first terminal device includes a processingunit and a sending unit, and functions of the processing unit and thesending unit may be corresponding to the method steps. Details are notdescribed herein again.

In another possible design, the first terminal device includes aprocessor, a memory, and a transmitter, and the processor, the memory,and the transmitter may be connected to each other through a bus system.The memory is configured to store a program, and the processor isconfigured to execute the program in the memory, to perform the methodperformed by the second terminal device in the second aspect or anypossible design of the second aspect.

According to a sixth aspect, an embodiment of this application providesa communications system, and the communications system includes thefirst terminal device in the second aspect and the second terminaldevice in the fourth aspect, or includes the first terminal device inthe third aspect or the second terminal device in the fifth aspect.

According to a seventh aspect, an embodiment of this applicationprovides a computer readable storage medium or a computer programproduct, configured to store a computer program. The computer program isused to perform the method in the first aspect and any possible designof the first aspect and in the second aspect and any possible design ofthe second aspect.

According to the system information transmission method and apparatusprovided in the embodiments of this application, when cell systeminformation changes, the first terminal device receives, during the onduration of the first terminal device, the system information sent bythe second terminal device, so that the first terminal device canreceive the system information through the sidelink between the firstterminal device and the second terminal device without a need tomaintain the cellular link, thereby reducing complexity and powerconsumption of system information transmission. Alternatively, when cellsystem information changes and the first terminal device has only onereceive radio frequency chain, the first terminal device may obtain thesystem information within the gap period of communication between thesecond terminal device and the first terminal device through the linkbetween the first terminal device and the network device. Communicationbetween the second terminal device and the first terminal device issuspended within the gap period, so that the changed system informationcan be received through the cellular link. In addition, the firstterminal device may maintain the cellular link only within the gapperiod, and does not need to maintain the cellular link within a periodother than the gap period, thereby reducing complexity and powerconsumption of system information transmission to some extent.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic architectural diagram of an application scenarioof a system information transmission method according to thisapplication;

FIG. 2 is an implementation flowchart of a system informationtransmission method according to an embodiment of this application;

FIG. 3 is an implementation flowchart of a method for transmittingsystem information by a first terminal device and a second terminaldevice on a paging occasion according to an embodiment of thisapplication;

FIG. 4 is an implementation flowchart of a method for transmittingsystem information by a first terminal device and a second terminaldevice by using a discovery message according to an embodiment of thisapplication;

FIG. 5 is an implementation flowchart of a method for transmittingsystem information by a first terminal device and a second terminaldevice by using an RRC message according to an embodiment of thisapplication;

FIG. 6 is another implementation flowchart of a system informationtransmission method according to an embodiment of this application;

FIG. 7 is a schematic structural diagram of a system informationtransmission apparatus according to an embodiment of this application;

FIG. 8 is a schematic structural diagram of a first terminal accordingto an embodiment of this application;

FIG. 9 is a schematic structural diagram of another system informationtransmission apparatus according to an embodiment of this application;

FIG. 10 is a schematic structural diagram of another first terminalaccording to an embodiment of this application;

FIG. 11 is a schematic structural diagram of still another systeminformation transmission apparatus according to an embodiment of thisapplication;

FIG. 12 is a schematic structural diagram of a second terminal accordingto an embodiment of this application;

FIG. 13 is a schematic structural diagram of still another systeminformation transmission apparatus according to an embodiment of thisapplication; and

FIG. 14 is a schematic structural diagram of another second terminalaccording to an embodiment of this application.

DESCRIPTION OF EMBODIMENTS

The following describes the embodiments of this application withreference to accompanying drawings.

A system information transmission method provided in the embodiments ofthis application may be applied to a communication scenario in which twodevices directly communicate with each other. In the embodiments of thisapplication, devices that directly communicate with each other mayinclude various handheld devices, in-vehicle devices, wearable devices,or computing devices with a wireless communication function, or otherprocessing devices connected to a wireless modem, and user equipment(User Equipment, UE) in various forms, mobile stations (Mobile station,MS) in various forms, terminals (terminal) in various forms, terminaldevices (Terminal Equipment) in various forms, and the like. For ease ofdescription, the devices that directly communicate with each other arereferred to as terminal devices below in the embodiments of thisapplication.

A UE-to-network relay scenario is a typical application scenario inwhich two devices directly communicate with each other. FIG. 1 is aschematic architectural diagram of the UE-to-network relay scenario. Inthe application scenario shown in FIG. 1 , a link between a networkdevice and a first terminal device and a link between the network deviceand a second terminal device may be referred to as cellular links or maybe referred to as an uplink and a downlink, and a link between the firstterminal device and the second terminal device may be referred to as asidelink. In this application, the second terminal device is a terminaldevice that directly interacts with the network device and may also bereferred to as a relay terminal device, and the first terminal device isa terminal device that communicates with the network device by using thesecond terminal device and may also be referred to as a remote terminaldevice. In existing layer 3 UE-to-network relay communication, controlsignaling of the first terminal device may interact with the networkdevice through a cellular link, and user data of the first terminaldevice may interact with the network device through a sidelink. That is,user data between the first terminal device and the network device maybe forwarded to the first terminal device by using the second terminaldevice, or user data between the second terminal device and the networkdevice may be forwarded to the network device by using the firstterminal device. In layer 2 UE-to-network relay communication, bothcontrol signaling and user data of the second terminal device mayinteract with the network device through a sidelink.

It may be understood that the network device in FIG. 1 is an apparatusthat is deployed in a radio access network and provides a wirelesscommunication function for a terminal, and may be a base station (basestation, BS), for example, may include various forms such as a macrobase station, a micro base station, a relay station, and an accesspoint. In a system using different radio access technologies, a name ofa device with a base station function may vary. For example, the deviceis referred to as an evolved NodeB (evolved NodeB, eNB or eNodeB forshort) in a long term evolution (Long Term Evolution, LTE) network, oris referred to as a NodeB (NodeB) in a third generation 3G network. Forease of description, in the embodiments of this application, the networkdevice that communicates with the first terminal device and the secondterminal device is referred to as a base station below.

Based on the application scenario shown in FIG. 1 , if systeminformation of a camped-on cell or a serving cell of the first terminaldevice and the second terminal device changes, or handover (handover)occurs between the first terminal device and the second terminal device,it may be understood that cell system information changes. In this case,the first terminal device and the second terminal device need tore-obtain the system information. The serving cell is a cell to which aterminal device is connected when the terminal device is in a radioresource control (Radio Resource Control, RRC) connected mode. Thecamped-on cell is a cell on which a terminal device camps when theterminal device is in an RRC idle mode. The system information is amessage that is periodically broadcast by the base station to allterminal devices in a cell on a broadcast channel. The systeminformation is classified into a master information block (MasterInformation Block, MIB) and a plurality of system information blocks(System Information Blocks, SIB). The master information block includesa limited quantity of most important and commonly used transmissionparameters for reading other cell information. The system informationblock includes other required parameters, including 20 systeminformation blocks: a SIB1 to a SIB20.

Based on the application scenario shown in FIG. 1 , for the firstterminal device, if a connection is established between the firstterminal device and the second terminal device, it may be consideredthat the first terminal device may camp on the second terminal deviceconnected to the first terminal device. When the cell system informationchanges, the first terminal device may obtain the system informationthrough a cellular link or may obtain the system information by usingthe second terminal device.

In an embodiment of this application, when cell system informationchanges, the first terminal device receives, during on duration of thefirst terminal device, system information sent by the second terminaldevice, so that the first terminal device can receive the systeminformation through a sidelink between the first terminal device and thesecond terminal device without a need to maintain a cellular link,thereby reducing complexity and power consumption of system informationtransmission.

In another embodiment of this application, when cell system informationchanges and the first terminal device has only one receive radiofrequency chain, the first terminal device may obtain system informationwithin a gap period between the second terminal device and the firstterminal device through a link between the first terminal device and thebase station. Communication between the second terminal device and thefirst terminal device is suspended within the gap period, so that thechanged system information can be received through a cellular link. Inaddition, the first terminal device may maintain the cellular link onlywithin the gap period, and does not need to maintain the cellular linkwithin a period other than the gap period, thereby reducing complexityand power consumption of system information transmission to some extent.

It may be understood that the system information transmission methodprovided in the embodiments of this application is not limited to theapplication scenario shown in FIG. 1 , and may also be applied to anapplication scenario in which two other devices directly communicatewith each other, for example, a short-range communication scenario inwhich a Bluetooth technology or a wireless fidelity (Wireless Fidelity,WiFi) technology is used.

The following describes a specific implementation method in which thefirst terminal device receives the system information by using thesecond terminal device or the cellular link with reference to actualapplication in the embodiments of this application.

FIG. 2 is an implementation flowchart of a system informationtransmission method according to an embodiment of this application.Referring to FIG. 2 , the method includes the following steps.

S101: A second terminal device determines on duration of a firstterminal device.

The on duration of the first terminal device is a time in which thefirst terminal device may send and receive a message. For example, theon duration may be a paging occasion (Paging Occasion, PO) of the firstterminal device in an RRC idle mode, or may be a time in which the firstterminal device receives a discovery message sent by the second terminaldevice, or may be a time in which the first terminal device in an RRCconnected mode receives a message sent by the second terminal device,including a time in which the first terminal device that is in an RRCconnected mode and is configured with discontinuous reception(Discontinuous Reception: DRX) is in DRX on duration (on duration), ormay be another time in which the first terminal device may receive amessage sent by the second terminal device. That the second terminaldevice determines the on duration of the first terminal device may beunderstood as that the second terminal device calculates the on durationof the first terminal device, or the second terminal device obtains aconfiguration of the on duration of the first terminal device.

S102: The second terminal device sends system information to the firstterminal device during the on duration of the first terminal device.

S103: The first terminal device receives, during the on duration of thefirst terminal device, the system information sent by the secondterminal device.

A part of system information delivered by a base station of a camped-oncell or a serving cell of the second terminal device is required by allfirst terminal devices that complete establishment of a direct link tothe second terminal device. In this embodiment of this application, thispart of system information may be referred to as basic systeminformation, for example, cell access related information IEcellAccessRelatedInfo in a SIB1. Another part of system informationdelivered by the base station of the camped-on cell or the serving cellof the second terminal device has different requirements for firstterminal devices of different types, capabilities, and servicerequirements. In this embodiment of this application, this part ofsystem information may be referred to as specific system information.For example, system information required by a first terminal device thatsupports extended access control (Extended access class barring, EAB) isa SIB14; system information required by a first terminal device thatsupports a multimedia broadcast multicast service (Multimedia BroadcastMulticast Service, MBMS) is a SIB13, a SIB15, and the like; and systeminformation required by a first terminal device that supportscollaboration between a universal mobile telecommunications system(Universal Mobile Telecommunication System, UMTS) evolved universalterrestrial radio access network (Evolved Universal Terrestrial RadioAccess Network, E-UTRAN) and a wireless local area network (WirelessLocal Area Networks, WLAN) is a SIB17 and the like. A first terminaldevice may not require specific system information, and specific systeminformation required by different first terminal devices may be the sameor partially the same.

System information that needs to be obtained by a first terminal deviceincludes basic system information and specific system informationrequired by the first terminal device, and the first terminal devicedoes not need to obtain specific system information of another firstterminal device. To reduce signaling overheads of transmitting systeminformation between the first terminal device and the second terminaldevice, the second terminal device may send, to the first terminaldevice, system information required by the first terminal device, wherethe system information required by the first terminal device may be apart or all of system information delivered by the base station of thecamped-on cell or the serving cell of the second terminal device. Thesecond terminal device may store specific system information required bythe first terminal device. The system information required by the firstterminal device may be changed system information in the systeminformation required by the first terminal device or all systeminformation required by the first terminal device.

When sending the system information to the first terminal device duringthe on duration of the first terminal device, the second terminal devicemay send the system information by using a broadcast address, in otherwords, send the system information to the first terminal device in abroadcast manner, so that all first terminal devices connected to thesecond terminal device can receive the system information. The secondterminal device may alternatively send the system information to thefirst terminal device by using a multicast address, in other words, sendthe system information to the first terminal device in a multicastmanner, so that some first terminal devices connected to the secondterminal device can receive the system information. The second terminaldevice may alternatively send the system information to the firstterminal device by using a unicast address, in other words, send thesystem information to the first terminal device in a unicast manner, sothat a first terminal device connected to the second terminal device canreceive the system information sent by the second terminal device.

In this embodiment of this application, when cell system informationchanges, the first terminal device receives, during the on duration ofthe first terminal device, the system information sent by the secondterminal device, so that the first terminal device can receive thesystem information through a sidelink between the first terminal deviceand the second terminal device without a need to maintain a cellularlink, thereby reducing complexity and power consumption of systeminformation transmission.

With reference to actual application, the embodiments of thisapplication describe below an implementation process of transmittingsystem information between the second terminal device and the firstterminal device in various scenarios in which the on duration of thefirst terminal is the paging occasion of the first terminal device, theon duration of the first terminal is a time in which the second terminaldevice sends the discovery message, and the on duration of the firstterminal is a time in which the first terminal device is in an RRCconnected mode and may receive the message sent by the second terminaldevice.

First, for a scenario in which on duration of a first terminal is apaging occasion of the first terminal device, an implementation processin which a second terminal sends system information to the firstterminal device on the paging occasion of the first terminal device, andthe first terminal device receives, on the paging occasion of the firstterminal, the system information sent by the second terminal device isdescribed.

FIG. 3 is an implementation flowchart of a method for transmittingsystem information by a first terminal device and a second terminaldevice on a paging occasion according to an embodiment of thisapplication. As shown in FIG. 3 , the method includes the followingsteps.

S201: A second terminal device determines a resource that is used tosend system information to a first terminal device on a paging occasionof the first terminal device.

In an implementation, the second terminal device may send the systeminformation to the first terminal device by using a dedicated resource.

The dedicated resource is determined by a base station based on adedicated resource requested by the second terminal device from the basestation and a time domain location that is of the paging occasion andthat is indicated by the second terminal device to the base station.

The second terminal device may request the dedicated resource from thebase station, and indicate the time domain location of the pagingoccasion, and the second terminal device indicates the time domainlocation of the paging occasion to the base station, so that the basestation allocates the dedicated resource to the paging occasioncorresponding to the time domain location. The second terminal deviceindicates the time domain location of the paging occasion to the basestation may be: the second terminal device may indicate, to the basestation, an S-temporary mobile subscriber identity (S-Temporary MobileSubscriber Identity, s-TMSI), a user equipment-specific discontinuousreception cycle (UE-specific DRX cycle), or a specific subframe indexsuch as 0, 4, 5, or 9, and other information that may be used todetermine the time domain location of the paging occasion, and the basestation may determine the time domain location of the paging occasion byusing the indicated information. The implementation in which the secondterminal device uses the dedicated resource is applicable to a scenarioin which the second terminal device is in an RRC connected mode.

In another implementation, the second terminal device may use a resourcein a sending resource pool that is configured or preconfigured by a basestation by using a broadcast message as a resource that is used by thesecond terminal device to send the system information to the firstterminal device.

In this embodiment of this application, a time domain location of theresource that is in the sending resource pool and that is used by thesecond terminal device overlaps with a time domain location of thepaging occasion of the first terminal device, so that when the secondterminal device sends the system information by using the resource inthe sending resource pool, the first terminal device can receive thesystem information sent by the second terminal device.

The resource in the sending resource pool may be a resource that is usedby the second terminal device to send a paging message. The secondterminal device may directly send the system information by using aresource that is used by a paging message originally sent by the secondterminal device, and use the sending resource used by the originalpaging message as the resource in the sending resource pool. The secondterminal device may alternatively add the system information to theoriginal paging message to obtain a new paging message, and use asending resource used by the new paging message as the resource in thesending resource pool.

The resource in the sending resource pool may be alternatively aresource that is specially used by the second terminal device to sendthe system information to the first terminal device. When a sendingresource pool that is specially used to send the system information isallocated to the second terminal device, the base station may schedule aresource in the resource pool to another terminal device for use whenthe second terminal device does not use the resource (when the systeminformation does not change), thereby reducing resource waste.

In this embodiment of this application, when the base station configuresthe sending resource pool for the second terminal device, the secondterminal device may be in an RRC connected mode or an RRC idle mode.Regardless of whether the second terminal device is in an RRC connectedmode or an RRC idle mode, the second terminal device can select, fromthe sending resource pool, a resource used for sending the systeminformation.

S202: The second terminal device sends the system information to thefirst terminal device on the paging occasion of the first terminaldevice by using a resource in a sending resource pool or by using adedicated resource, where the sending resource pool is configured orpreconfigured by a base station by using a broadcast message, and thededicated resource is configured by the base station for the secondterminal device.

In this embodiment of this application, the second terminal device maysend the system information on one or more paging occasions of the firstterminal device, to ensure that the first terminal device can receivethe system information sent by the second terminal device. The secondterminal device may send the system information on the one or morepaging occasions of the first terminal device in a broadcast manner, orthe second terminal device may send the system information on the one ormore paging occasions of the first terminal device in a multicastmanner, or the second terminal device may send the system information onthe one or more paging occasions of the first terminal device in aunicast manner.

In this embodiment of this application, the second terminal device maysend only changed system information to the first terminal device,thereby reducing signaling overheads. The second terminal device mayobtain the changed system information in one of the following manners:

A: The base station indicates the changed system information in a pagingmessage, and the second terminal device may determine the changed systeminformation by receiving a paging message sent by the base station. Thebase station may indicate the changed system information in the pagingmessage in the following manner: extending IE system Info Modificationto indicate the changed system information in content of the IE systemInfo Modification; or newly adding an IE to indicate the changed systeminformation in content of the newly added IE.

B: The base station indicates the changed system information in a SIB1message, and the second terminal device may determine the changed systeminformation by receiving a SIB1 message sent by the base station. Thebase station may indicate the changed system information in the SIB1message in the following manner: extending IE system Info Value Tag toindicate the changed system information in content of the IE system InfoValue Tag; or newly adding an IE to indicate the changed systeminformation in content of the newly added IE.

C: The second terminal device receives system information sent by thebase station, and compares the newly received system information withcurrently stored original system information, to further determine thechanged system information.

In the two manners A and B of determining the changed systeminformation, the second terminal device may receive only the changedsystem information without a need to compare system information, therebyreducing power consumption.

In this embodiment of this application, the method may further includethe following step S203:

S203: The second terminal device sends indication information to thefirst terminal device, where the indication information is used toindicate that the system information changes. The indication informationmay indicate that the system information changes, or indicate a primarynotification and/or a secondary notification of an earthquake andtsunami warning system (Earthquake and Tsunami Warning System, ETWS), orindicate a commercial mobile alert service (Commercial Mobile AlertService, CMAS) notification, or indicate that an extended access barring(Extended Access Barring, EAB) parameter changes, or the like. Theindication information may be carried in a paging message, or may becarried in a discovery message, or may be carried in a newly addedmessage. In this embodiment of this application, S203 is an optionalstep. When step S203 is included, the second terminal device sends, tothe first terminal device, the indication information that is used toindicate that the system information changes, so that the first terminaldevice receives the system information only when the first terminaldevice needs to receive the system information, thereby reducingsignaling overheads.

S204: The first terminal device determines the paging occasion of thefirst terminal device, and receives, on the paging occasion of the firstterminal device, the system information sent by the second terminaldevice by using the resource in the sending resource pool or by usingthe dedicated resource.

In this embodiment of this application, the second terminal device sendsthe system information to the first terminal device on the pagingoccasion of the first terminal device, so that the first terminal devicecan receive the system information through a sidelink between the firstterminal device and the second terminal device without a need tomaintain a cellular link, thereby reducing complexity and powerconsumption of system information transmission. In addition, the secondterminal device sends the system information to the first terminaldevice on the paging occasion of the first terminal device, andregardless of whether the first terminal device is in an RRC connectedmode or an RRC idle mode, the first terminal device can receive thesystem information sent by the second terminal device. This embodimentcan be applied to wide scenarios.

Second, in an embodiment of this application, for a scenario in which onduration of a first terminal is a time in which the second terminaldevice sends a discovery message, an implementation process in which thesecond terminal adds system information to the discovery message sent bythe second terminal device and sends the discovery message to the firstterminal device, and the first terminal obtains the system informationby receiving the discovery message sent by the second terminal device isdescribed.

FIG. 4 is an implementation flowchart of a method for transmittingsystem information by a first terminal device and a second terminaldevice by using a discovery message according to an embodiment of thisapplication. As shown in FIG. 4 , the method includes the followingsteps.

S301: A second terminal device determines a discovery message that isused to send system information.

In this embodiment of this application, the second terminal device mayadd the system information to a reserved bit in an existing discoverymessage, or the second terminal device may establish a discovery messagethat is specially used for carrying the system information. A bit in thediscovery message that is specially used for carrying the systeminformation may carry the system information, and carry some necessaryinformation such as a destination address.

In this embodiment of this application, the second terminal device mayadd the system information to one or more discovery messages.

S302: The second terminal device broadcasts the system information to afirst terminal device by using the discovery message.

S303: The first terminal device receives, within a time of receiving thediscovery message sent by the second terminal device, the discoverymessage that is sent by the second terminal device and that carries thesystem information. The first terminal device needs to receive thediscovery message regardless of whether the first terminal device is inan RRC connected mode or an RRC idle mode.

In this embodiment of this application, the second terminal device addsthe system information to the discovery message and sends the discoverymessage to the first terminal device, so that the first terminal devicecan receive the system information through a sidelink between the firstterminal device and the second terminal device without a need tomaintain a cellular link, thereby reducing complexity and powerconsumption of system information transmission.

Third, in an embodiment of this application, for a scenario in which onduration of a first terminal device is a time in which the firstterminal device in an RRC connected mode receives a message sent by asecond terminal device, including a time in which the first terminaldevice that is in an RRC connected mode and that is configured withdiscontinuous reception (Discontinuous Reception: DRX) is in DRX onduration (on duration), an implementation process in which the secondterminal device forwards, to the first terminal device, an RRC messagethat is sent by a base station and that carries system information, andthe first terminal obtains the system information by receiving the RRCmessage that is sent by the base station and that is forwarded by thesecond terminal device is described.

FIG. 5 is an implementation flowchart of a method for transmittingsystem information by a first terminal device and a second terminaldevice by using an RRC message according to an embodiment of thisapplication. As shown in FIG. 5 , the method includes the followingsteps.

S401: A base station determines that system information changes, andadds system information required by a first terminal device to an RRCmessage.

The RRC message that carries the system information required by thefirst terminal device may be an RRC dedicated message.

Specifically, the system information required by the first terminaldevice may be carried in an RRC reconfiguration message in the RRCdedicated message, and the RRC reconfiguration message that carries thesystem information required by the first terminal device may be sent tothe first terminal device by using a layer 2 relay protocol stack.

S402: The base station sends, to a second terminal device, the RRCmessage that carries the system information required by the firstterminal device.

S403: The second terminal device receives the RRC message sent by thebase station, and forwards, to the first terminal device, the RRCmessage that carries the system information required by the firstterminal device.

S404: The first terminal device receives the RRC message that carriesthe system information required by the first terminal device, andobtains the required system information.

In this embodiment of this application, the second terminal device needsto obtain a resource that is used to forward the RRC message to thefirst terminal device. To reduce signaling overheads of requesting aresource and allocating a resource by the second terminal device, thebase station may configure, for the RRC message that is sent to thesecond terminal device and that carries the system information requiredby the first terminal device, the resource that is used to forward theRRC message.

In this embodiment of this application, the second terminal deviceforwards, to the first terminal device, the RRC message that is sent bythe base station and that carries the system information, so that thefirst terminal device can receive the system information through asidelink between the first terminal device and the second terminaldevice without a need to maintain a cellular link, thereby reducingcomplexity and power consumption of system information transmission. Inaddition, in the solution in which the system information is carried inthe RRC message, regardless of whether the first terminal device is incoverage of a cell or is out of coverage of a cell, the first terminaldevice can obtain the system information in this manner as long as thefirst terminal device is in an RRC connected mode. An implementationprocess is simple, and an existing standard protocol is slightlychanged, thereby reducing signaling overheads and resource waste.

In this embodiment of this application, when cell system informationchanges, and the second terminal device determines that the cell systeminformation changes, the second terminal device may send a direct linkrelease message (DIRECT_COMMUNICATION_RELEASE) to the first terminaldevice in an RRC idle mode, and indicate that a reason for releasing alink is that the system information changes. After receiving the directlink release message, the first terminal device determines, based on thedirect link release message, that the system information changes. Thefirst terminal device releases a direct link between the first terminaldevice and the second terminal device, re-establishes the direct linkbetween the first terminal device and the second terminal device, andobtains the changed system information when or after the direct linkbetween the first terminal device and the second terminal device isre-established, or a camped-on cell or a serving cell that camps on thesecond terminal device receives the changed system information through acellular link.

In another embodiment of this application, when cell system informationchanges and the first terminal device has only one receive radiofrequency chain, the first terminal device may obtain the systeminformation within a gap period of communication between the secondterminal device and the first terminal device through a link between thefirst terminal device and the base station.

FIG. 6 is another implementation flowchart of a system informationtransmission method according to an embodiment of this application. Asshown in FIG. 6 , the method includes the following steps.

S501: A second terminal device determines that system informationrequired by a first terminal device changes, and the second terminaldevice sends indication information to the first terminal device, wherethe indication information is used to indicate that the systeminformation changes.

The indication information may indicate that the system informationchanges, or indicate a primary notification and/or a secondarynotification of an earthquake and tsunami warning system ETWS, orindicate a commercial mobile alert service CMAS notification, orindicate that an extended access barring EAB parameter changes, or thelike. The indication information may be carried in a paging message, ormay be carried in a discovery message, or may be carried in a newlyadded message.

The indication information may be a paging message that is sent by thesecond terminal device to the first terminal device and that is used toindicate that the system information changes. The paging message that isused to indicate that the system information changes may include IEsystem Info Modification and IE system Info Modification is set to true,to indicate that the system information changes. The paging message thatis used to indicate that the system information changes may furtherinclude IE etws-Indication and IE etws-Indication is set to true, toindicate that earthquake and tsunami warning system (Earthquake andTsunami Warning System, ETWS) system information changes. Alternatively,the paging message that is used to indicate that the system informationchanges may further include IE cmas-Indication and IE cmas-Indication isset to true, to indicate that commercial mobile alert service(Commercial Mobile Alert Service, CMAS) system information changes, orthe paging message that is used to indicate that the system informationchanges may further include IE eab-Param Modification and IE eab-ParamModification is set to true, to indicate that extended access barring(Extended Access Barring, EAB) system information changes.

S502: The first terminal device receives the indication information sentby the second terminal device, and obtains the system informationaccording to the indication information.

The first terminal device may receive the system information through asidelink between the first terminal device and the second terminaldevice according to the indication information.

If the first terminal device has only one receive radio frequency chain(RX chain), the first terminal device may obtain the system informationaccording to the indication information within a gap period ofcommunication between the second terminal device and the first terminaldevice through a link between the first terminal device and a basestation. Communication between the second terminal device and the firstterminal device is suspended within the gap period. The second terminaldevice and the first terminal device may still communicate with eachother through the sidelink outside the gap period. It should be notedthat the gap period is to distinguish between a time of communicationbetween the first terminal device and the second terminal device and atime of communication between the first terminal device and the basestation. It may be understood that, in another possible implementation,the second terminal device communicates with the first terminal devicewithin the gap period, and communication between the second terminaldevice and the first terminal device is suspended within the gap period.

In this embodiment of this application, if the first terminal device isin an RRC idle mode and has no data service, the gap period may beconfigured by the first terminal device, or may be configured orpreconfigured by the second terminal device. A time domain location ofthe gap period configured by the first terminal device does not overlapwith a time domain location of on duration of the first terminal devicesuch as a paging occasion of the first terminal, in other words, thefirst terminal device may select any time period in a sleep time of thefirst terminal device as the gap period, and switch to a cellular linkwithin the gap period to receive the system information. A time domainlocation of the gap period configured by the second terminal device doesnot overlap with a time domain location of on duration of the firstterminal device such as a paging occasion of the first terminal, inother words, the second terminal device may select any time period in asleep time of the first terminal device as the gap period, and switch toa cellular link within the gap period to receive the system information.

If the first terminal device is in an RRC connected mode, the gap periodmay be configured by the second terminal device or the base station forthe first terminal device. If the gap period is configured by the basestation, the base station needs to forward configuration information ofthe gap period to the second terminal device. If the gap period isconfigured by the second terminal device, the second terminal device maysend configuration information of the gap period to the base station.The second terminal device or the base station may control not to senddata to the first terminal device within the gap period, or the secondterminal device or the base station may control not to schedule thefirst terminal device within the gap period. The gap period configuredby the second terminal device or the base station for the first terminaldevice may be one or more modification periods, or may be periods ofsome system information windows (SI window), or may be a periodicallyrepeated time period, or may be another customized time period.

In a possible implementation, to enable the first terminal device toaccurately and quickly switch to a cellular link to obtain the systeminformation, the first terminal device needs to obtain a cell identifierof a serving cell of the second terminal device. Therefore, in thisembodiment of this application, before the system information isobtained through the link between the first terminal device and the basestation, the first terminal device may obtain a cell identifier of acell in which the second terminal device is located. Certainly, in thisembodiment of this application, in addition to obtaining the cellidentifier, the first terminal device may obtain other assistanceinformation that helps the first terminal device quickly find the cellin which the second terminal device is located.

In another possible implementation, in addition to sending, to the firstterminal device, the indication information that is used to indicatethat the system information changes, the second terminal device mayindicate the changed system information to the first terminal, forexample, one or more SIBs change or one or more IEs in a SIB change, andthe changed system information may be carried in the indicationinformation, so that the first terminal device needs to receive only thesystem information required by the first terminal device, and does notneed to receive all system information, thereby reducing signalingoverheads.

In this embodiment of this application, when cell system informationchanges, and the first terminal device has only one receive radiofrequency chain, the first terminal device may suspend communicationwithin the gap period of communication between the second terminaldevice and the first terminal device, and obtain the system informationthrough the link between the first terminal device and the base station,to receive the changed system information through the cellular link. Inaddition, the first terminal device may maintain the cellular link onlywithin the gap period, and does not need to maintain the cellular linkwithin a period other than the gap period, thereby reducing complexityand power consumption of system information transmission to some extent.

The foregoing mainly describes the solutions provided in the embodimentsof this application from the perspective of interaction between thefirst terminal device and the second terminal device. It may beunderstood that to implement the foregoing functions, the first terminaldevice and the second terminal device include corresponding hardwarestructures and/or software units for performing the functions. Withreference to the units and the algorithm steps in the examples describedin the embodiments disclosed in this application, the embodiments ofthis application can be implemented by hardware or a combination ofhardware and computer software. Whether a function is performed byhardware or hardware driven by computer software depends on particularapplications and design constraints of the technical solutions. A personskilled in the art may use different methods to implement the describedfunctions for each particular application, but it should not beconsidered that the implementation falls beyond the scope of thetechnical solutions in the embodiments of this application.

In the embodiments of this application, functional units of the firstterminal device and the second terminal device may be obtained throughdivision based on the foregoing method examples. For example, eachfunctional unit may be obtained through division based on eachcorresponding function, or two or more functions may be integrated intoone processing unit. The integrated unit may be implemented in a form ofhardware, or may be implemented in a form of a software functional unit.It should be noted that in the embodiments of this application, unitdivision is an example and is merely logical function division. Inactual implementation, another division manner may be used.

Based on a same concept as the foregoing method embodiment, anembodiment of this application provides a system informationtransmission apparatus.

When an integrated unit is used, FIG. 7 is a schematic diagram of apossible logical structure of a system information transmissionapparatus 100. The system information transmission apparatus 100 may beapplied to a first terminal device. Referring to FIG. 7 , the systeminformation transmission apparatus 100 applied to the first terminaldevice includes a processing unit 101 and a receiving unit 102. Theprocessing unit 101 is configured to determine on duration of the firstterminal device. The receiving unit 102 is configured to receive, duringthe on duration of the first terminal device determined by theprocessing unit 101, system information sent by a second terminaldevice.

The system information is system information required by the firstterminal device, and the system information required by the firstterminal device is a part or all of system information delivered by abase station of a camped-on cell or a serving cell of the secondterminal device.

The system information required by the first terminal device includeschanged system information in the system information required by thefirst terminal device or all system information required by the firstterminal device.

In a possible implementation, the receiving unit 102 receives, on apaging occasion of the first terminal device, the system informationsent by the second terminal device at least one time by using a resourcein a sending resource pool, where the sending resource pool isconfigured or preconfigured by the base station by using a broadcastmessage.

The resource in the sending resource pool is a resource that is used bythe second terminal device to send a paging message, or the resource inthe sending resource pool is a resource that is specially used by thesecond terminal device to send the system information to the firstterminal device.

In another possible implementation, the receiving unit 102 receives, ona paging occasion of the first terminal device, the system informationsent by the second terminal device at least one time by using adedicated resource, where the dedicated resource is configured by thebase station for the second terminal device.

The dedicated resource is determined by the base station based on adedicated resource requested by the second terminal device from the basestation and an indicated time domain resource location of the pagingoccasion.

In still another possible implementation, the on duration of the firstterminal device is a time in which the first terminal receives adiscovery message sent by the second terminal device, and the systeminformation is carried in the discovery message sent by the secondterminal device.

In still another possible implementation, the on duration of the firstterminal device is a time in which the first device is in an RRCconnected mode and may receive a message sent by the second terminaldevice, and the system information is carried in an RRC message that issent by the base station and that is forwarded by the second terminaldevice.

In still another possible implementation, the receiving unit 102 isfurther configured to:

before receiving the system information sent by the second terminaldevice, receive indication information sent by the second terminaldevice, where the indication information is used to indicate that thesystem information changes.

In still another possible implementation, the on duration of the firstterminal device is a time in which the first terminal receives adiscovery message sent by the second terminal device, and the systeminformation is carried in the discovery message sent by the secondterminal device.

When a form of hardware is used, the processing unit 101 may be aprocessor or a controller, and the receiving unit 102 may be acommunications interface, a receiver, a transceiver circuit, or thelike. The communications interface is a generic term, and may includeone or more interfaces.

When the processing unit 101 is the processor and the receiving unit 102is the receiver, the system information transmission apparatus 100 inthis embodiment of this application may be a first terminal device shownin FIG. 8 . The first terminal device shown in FIG. 8 may be a wearabledevice.

FIG. 8 is a schematic diagram of a first terminal device 1000 accordingto an embodiment of this application. The first terminal device 1000 maybe configured to perform the method performed by the first terminaldevice in FIG. 2 to FIG. 5 . As shown in FIG. 8 , the first terminaldevice 1000 includes a processor 1001, a memory 1002, and a receiver1003. The processor 1001, the memory 1002, and the receiver 1003 may beconnected to each other through a bus system. The memory 1002 isconfigured to store a program, an instruction, or code. The processor1001 is configured to execute the program in the memory 1002 to performthe following operations: controlling the receiver 1003 to receive,during on duration of the first terminal device, system information sentby a second terminal device, and implementing the steps and thefunctions implemented by the first terminal device in the foregoingimplementations. Details are not described herein again.

For specific implementations of the processor 1001 and the receiver1003, refer to specific descriptions of the processing unit 101 and thereceiving unit 102 in the foregoing implementations in FIG. 7 . Detailsare not described herein again.

Based on a same concept as the foregoing method embodiment, anembodiment of this application further provides a system informationtransmission apparatus.

When an integrated unit is used, FIG. 9 is a schematic diagram of alogical structure of a system information transmission apparatus 200according to an embodiment of this application. The system informationtransmission apparatus 200 may be applied to a first terminal device.Referring to FIG. 9 , the system information transmission apparatus 200applied to the first terminal device includes a receiving unit 201 and aprocessing unit 202. The receiving unit 201 is configured to receiveindication information sent by a second terminal device, where theindication information is used to indicate that system informationchanges. The processing unit 202 obtains the system informationaccording to the indication information received by the receiving unit201.

In a possible implementation, the processing unit 202 is configured to:when the receiving unit 201 receives the indication information, obtainthe system information within a gap period of communication between thesecond terminal device and the first terminal device through a linkbetween the first terminal device and a base station, wherecommunication between the second terminal device and the first terminaldevice is suspended within the gap period.

If the first terminal device is in an RRC idle mode, the gap period isconfigured by the first terminal device or the second terminal device,or if the first terminal device is in an RRC connected mode, the gapperiod is configured by the second terminal device or the base stationfor the first terminal device.

In another possible implementation, the receiving unit 201 is furtherconfigured to: before the processing unit 202 obtains the systeminformation within the gap period through the link between the firstterminal device and the base station, obtain a cell identifier of a cellin which the second terminal device is located.

In still another possible implementation, the indication information isfurther used to indicate a type of the changed system information.

In still another possible implementation, the processing unit 202 isconfigured to: when the receiving unit 201 receives the indicationinformation, obtain the system information through a link between thefirst terminal device and the second terminal device.

When a form of hardware is used, the receiving unit 201 may be acommunications interface, a receiver, a transceiver circuit, or thelike. The communications interface is a generic term, and may includeone or more interfaces. The processing unit 202 may be a processor or acontroller.

When the processing unit 202 is the processor and the receiving unit 201is the receiver, the system information transmission apparatus 200 inthis embodiment of this application may be a first terminal device shownin FIG. 10 . The first terminal device shown in FIG. 10 may be awearable device.

FIG. 10 is a schematic diagram of a first terminal device 2000 accordingto an embodiment of this application. The first terminal device 2000 maybe configured to perform the method performed by the first terminaldevice in FIG. 6 . As shown in FIG. 10 , the first terminal device 2000includes a processor 2001, a memory 2002, and a receiver 2003. Theprocessor 2001, the memory 2002, and the receiver 2003 may be connectedto each other through a bus system. The memory 2002 is configured tostore a program, an instruction, or code. The processor 2001 isconfigured to execute the program in the memory 2002 to perform thefollowing operations: controlling the receiver 2003 to receiveindication information sent by a second terminal device, performing astep of obtaining system information according to the indicationinformation, and implementing the steps and the functions implemented bythe first terminal device in the foregoing implementations. Details arenot described herein again.

For specific implementations of the processor 2001 and the receiver2003, refer to specific descriptions of the processing unit 202 and thereceiving unit 201 in the foregoing implementations in FIG. 9 . Detailsare not described herein again.

Based on a same concept as the foregoing method embodiment, anembodiment of this application further provides a system informationtransmission apparatus.

When an integrated unit is used, FIG. 11 is a schematic diagram of alogical structure of a system information transmission apparatus 300according to an embodiment of this application. The system informationtransmission apparatus 300 may be applied to a second terminal device.Referring to FIG. 11 , the system information transmission apparatus 300applied to the second terminal device includes a processing unit 301 anda sending unit 302. The processing unit 301 is configured to determineon duration of a first terminal device. The sending unit 302 isconfigured to send system information to the first terminal deviceduring the on duration of the first terminal device determined by theprocessing unit 301.

The system information is system information required by the firstterminal device, and the system information required by the firstterminal device is a part or all of system information delivered by abase station of a camped-on cell or a serving cell of the secondterminal device.

The system information required by the first terminal device includeschanged system information in the system information required by thefirst terminal device or all system information required by the firstterminal device.

In a possible implementation, the sending unit 302 sends the systeminformation at least one time on a paging occasion of the first terminaldevice by using a resource in a sending resource pool, where the sendingresource pool is configured or preconfigured by the base station byusing a broadcast message.

The resource in the sending resource pool is a resource that is used bythe second terminal device to send a paging message, or the resource inthe sending resource pool is a resource that is specially used by thesecond terminal device to send the system information to the firstterminal device.

In another possible implementation, the sending unit 302 sends thesystem information at least one time on a paging occasion of the firstterminal device by using a dedicated resource, where the dedicatedresource is configured by the base station for the second terminaldevice.

The dedicated resource is determined by the base station based on adedicated resource requested by the second terminal device from the basestation and an indicated time domain resource location of the pagingoccasion.

In still another possible implementation, the on duration of the firstterminal device is a time in which the second terminal device sends adiscovery message, and the system information is carried in thediscovery message sent by the second terminal device.

In still another possible implementation, the on duration of the firstterminal device is a time in which the first device is in an RRCconnected mode and may receive a message sent by the second terminaldevice, and the system information is carried in an RRC message that issent by the base station and that is forwarded by the second terminaldevice.

In still another possible implementation, the sending unit 302 isfurther configured to send indication information to the first terminaldevice before sending the system information to the first terminaldevice, where the indication information is used to indicate that thesystem information changes.

When a form of hardware is used, the processing unit 301 may be aprocessor or a controller, and the sending unit 302 may be acommunications interface, a transmitter, a transceiver circuit, or thelike. The communications interface is a generic term, and may includeone or more interfaces.

When the processing unit 301 is the processor and the sending unit 302is the transmitter, the system information transmission apparatus 300 inthis embodiment of this application may be a second terminal deviceshown in FIG. 12 . The second terminal device shown in FIG. 12 may be anintelligent mobile terminal.

FIG. 12 is a schematic diagram of a second terminal device 3000according to an embodiment of this application. The second terminaldevice 3000 may be configured to perform the method performed by thesecond terminal device in FIG. 2 to FIG. 5 . As shown in FIG. 12 , thesecond terminal device 3000 includes a processor 3001, a memory 3002,and a transmitter 3003. The processor 3001, the memory 3002, and thetransmitter 3003 may be connected to each other through a bus system.The memory 3002 is configured to store a program, an instruction, orcode. The processor 3001 is configured to execute the program in thememory 3002 to perform the following operations: determining on durationof a first terminal device, controlling the transmitter 3003 to sendsystem information to the first terminal device during the on durationof the first terminal device, and implementing the steps and thefunctions implemented by the second terminal device in the foregoingimplementations. Details are not described herein again.

For specific implementations of the processor 3001 and the transmitter3003, refer to specific descriptions of the processing unit 301 and thesending unit 302 in the foregoing implementations in FIG. 11 . Detailsare not described herein again.

Based on a same concept as the foregoing method embodiment, anembodiment of this application further provides a system informationtransmission apparatus.

When an integrated unit is used, FIG. 13 is a schematic diagram of alogical structure of a system information transmission apparatus 400according to an embodiment of this application. The system informationtransmission apparatus 400 may be applied to a second terminal device.Referring to FIG. 13 , the system information transmission apparatus 400applied to the second terminal device includes a processing unit 401 anda sending unit 402. The processing unit 401 is configured to determinethat system information required by a first terminal device changes. Thesending unit 402 is configured to send indication information to thefirst terminal device when the processing unit 401 determines that thesystem information required by the first terminal device changes, wherethe indication information is used to indicate that the systeminformation changes.

The indication information may be a paging message that is sent by thesecond terminal device to the first terminal device and that is used toindicate that the system information changes.

In a possible implementation, the processing unit 401 is furtherconfigured to: if the first terminal device is in an RRC connected mode,configure a gap period of communication between the second terminaldevice and the first terminal device for the first terminal device,where communication between the second terminal device and the firstterminal device is suspended within the gap period, and the firstterminal device obtains the system information through a link betweenthe first terminal device and a base station.

The processing unit 401 is further configured to:

if the first terminal device is in an RRC idle mode, configure a gapperiod of communication between the second terminal device and the firstterminal device for the first terminal device; or if the first terminaldevice is in an RRC connected mode, configure a gap period ofcommunication between the second terminal device and the first terminaldevice for the first terminal device.

The sending unit 402 is further configured to: if the first terminaldevice is in an RRC connected mode, forward a gap period ofcommunication between the second terminal device and the first terminaldevice that is configured by a network device for the first terminaldevice, where

communication between the second terminal device and the first terminaldevice is suspended within the gap period, and the first terminal deviceobtains the system information through a link between the first terminaldevice and the network device.

In still another possible implementation, the indication information isfurther used to indicate a type of the changed system information.

In still another possible implementation, the sending unit 402 isfurther configured to send the system information to the first terminaldevice through a link between the first terminal device and the secondterminal device.

When a form of hardware is used, the processing unit 401 may be aprocessor or a controller, and the sending unit 402 may be acommunications interface, a transmitter, a transceiver circuit, or thelike. The communications interface is a generic term, and may includeone or more interfaces.

When the processing unit 401 is the processor and the sending unit 402is the transmitter, the system information transmission apparatus 400 inthis embodiment of this application may be a second terminal deviceshown in FIG. 14 . The second terminal device shown in FIG. 14 may be anintelligent mobile terminal.

FIG. 14 is a schematic diagram of a second terminal device 4000according to an embodiment of this application. The second terminaldevice 4000 may be configured to perform the method performed by thesecond terminal device in FIG. 6 . As shown in FIG. 14 , the secondterminal device 4000 includes a processor 4001, a memory 4002, and atransmitter 4003. The processor 4001, the memory 4002, and thetransmitter 4003 may be connected to each other through a bus system.The memory 4002 is configured to store a program, an instruction, orcode. The processor 4001 is configured to execute the program in thememory 4002 to perform the following operations: when determining thatsystem information required by a first terminal device changes,controlling the transmitter 4003 to send indication information to thefirst terminal device, where the indication information is used toindicate that the system information changes; and implementing the stepsand the functions implemented by the second terminal device in theforegoing implementations. Details are not described herein again.

For specific implementations of the processor 4001 and the transmitter4003, refer to specific descriptions of the processing unit 401 and thesending unit 402 in the foregoing implementations in FIG. 13 . Detailsare not described herein again.

It may be understood that the embodiments of this application showmerely simplified designs of the first terminal device and the secondterminal device. In actual application, the first terminal device andthe second terminal device are not limited to the foregoing structures.For example, the first terminal device may further include atransmitter, and the second terminal device may further include areceiver. In actual application, the first terminal device and thesecond terminal device each may include any quantity of receivers,transmitters, processors, memories, and the like, and all terminals thatcan implement the embodiments of this application shall fall within theprotection scope of the embodiments of this application.

It may be further understood that the first terminal device and thesecond terminal device in the embodiments of this application may beconfigured to implement the corresponding functions of the firstterminal device and the second terminal device in the method embodimentsin the embodiments of this application. Therefore, for a part that isnot described in detail in the embodiments of this application, refer torelated descriptions in the method embodiments. Details are notdescribed in the embodiments of this application again.

It may be further understood that in the embodiment of this application,the processor may be a central processing unit (Central Processing Unit,CPU), or may be another general purpose processor, a digital signalprocessor (DSP), an application-specific integrated circuit (ASIC), afield programmable gate array (FPGA), another programmable logic device,a discrete gate, a transistor logic device, a discrete hardwarecomponent, or the like. The general purpose processor may be amicroprocessor, or the processor may be any conventional processor orthe like.

The memory may include a read-only memory and a random access memory,and provide an instruction and data for the processor. A part of thememory may further include a non-volatile random access memory. Forexample, the memory may further store device type information.

The bus system may include a power bus, a control bus, a status signalbus, and the like in addition to a data bus. However, for cleardescription, various types of buses in the figure are marked as the bussystem.

In an implementation process, the steps in the foregoing methodembodiments may be completed by using a hardware integrated logiccircuit in the processor or by using an instruction in a form ofsoftware. The steps of the system information transmission methoddisclosed with reference to the embodiments of this application may bedirectly performed by a hardware processor, or may be performed by usinga combination of hardware in the processor and a software module. Thesoftware module may be located in a mature storage medium in the art,such as a random access memory, a flash memory, a read-only memory, aprogrammable read-only memory, an electrically erasable programmablememory, or a register. The storage medium is located in the memory, andthe processor reads information in the memory and completes the steps inthe foregoing method embodiments in combination with hardware in theprocessor. To avoid repetition, details are not described herein again.

An embodiment of this application provides a communications system, andthe communications system includes the foregoing first terminal deviceand the foregoing second terminal device.

An embodiment of this application provides a computer readable storagemedium or a computer program product, configured to store a computerprogram. The computer program is used to perform the method in anypossible implementation of the foregoing method embodiments.

According to the system information transmission method and apparatusprovided in the embodiments of this application, when cell systeminformation changes, the first terminal device receives, during the onduration of the first terminal device, the system information sent bythe second terminal device, so that the first terminal device canreceive the system information through a sidelink between the firstterminal device and the second terminal device without a need tomaintain a cellular link, thereby reducing complexity and powerconsumption of system information transmission. Alternatively, when cellsystem information changes and the first terminal device has only onereceive radio frequency chain, the first terminal device may obtain thesystem information within the gap period of communication between thesecond terminal device and the first terminal device through the linkbetween the first terminal device and the base station. Communicationbetween the second terminal device and the first terminal device issuspended within the gap period, so that the changed system informationcan be received through a cellular link. In addition, the first terminaldevice may maintain the cellular link only within the gap period, anddoes not need to maintain the cellular link within a period other thanthe gap period, thereby reducing complexity and power consumption ofsystem information transmission to some extent.

A person skilled in the art should understand that the embodiments ofthis application may be provided as a method, a system, or a computerprogram product. Therefore, the embodiments of this application may usea form of hardware only embodiments, software only embodiments, orembodiments with a combination of software and hardware. Moreover, theembodiments of this application may use a form of a computer programproduct that is implemented on one or more computer-usable storage media(including but not limited to a magnetic disk memory, a CD-ROM, anoptical memory, and the like) that include computer-usable program code.

The embodiments of this application are described with reference to theflowcharts and/or the block diagrams of the method, the device (system),and the computer program product according to the embodiments of thisapplication. It should be understood that computer program instructionsmay be used to implement each process and/or each block in theflowcharts and/or the block diagrams and a combination of a processand/or a block in the flowcharts and/or the block diagrams. Thesecomputer program instructions may be provided for a general-purposecomputer, a dedicated computer, an embedded processor, or a processor ofany other programmable data processing device to generate a machine, sothat the instructions executed by a computer or a processor of any otherprogrammable data processing device generate an apparatus forimplementing a specific function in one or more processes in theflowcharts and/or in one or more blocks in the block diagrams.

These computer program instructions may be stored in a computer readablememory that can instruct the computer or any other programmable dataprocessing device to work in a specific manner, so that the instructionsstored in the computer readable memory generate an artifact thatincludes an instruction apparatus. The instruction apparatus implementsa specific function in one or more processes in the flowcharts and/or inone or more blocks in the block diagrams.

These computer program instructions may be loaded onto a computer oranother programmable data processing device, so that a series ofoperations and steps are performed on the computer or the anotherprogrammable device, thereby generating computer-implemented processing.Therefore, the instructions executed on the computer or the anotherprogrammable device provide steps for implementing a specific functionin one or more processes in the flowcharts and/or in one or more blocksin the block diagrams.

What is claimed is:
 1. A system information transmission method,comprising: determining, by a first terminal device, an on duration ofthe first terminal device, wherein the on duration of the first terminaldevice is a time in which the first terminal device is configured toreceive a message sent by a second terminal device; and receiving, bythe first terminal device during the on duration of the first terminaldevice, system information sent by the second terminal device through asidelink between the first terminal device and the second terminaldevice without a need to maintain a cellular link.
 2. The methodaccording to claim 1, wherein the on duration of the first terminaldevice is a paging occasion of the first terminal device.
 3. The methodaccording to claim 2, wherein receiving, by the first terminal deviceduring the on duration of the first terminal device, the systeminformation sent by the second terminal device further comprises:receiving, by the first terminal device on the paging occasion of thefirst terminal device, the system information sent by the secondterminal device at least one time by using a resource in a sendingresource pool, wherein the sending resource pool is configured orpreconfigured by a network device by using a broadcast message; orreceiving, by the first terminal device on the paging occasion of thefirst terminal device, the system information sent by the secondterminal device at least one time by using a dedicated resource, whereinthe dedicated resource is configured by a network device for the secondterminal device.
 4. The method according to claim 1, wherein the systeminformation is carried in a radio resource control (RRC) message that issent by a network device and the RRC message is forwarded by the secondterminal device.
 5. The method according to claim 1, wherein beforereceiving, by the first terminal device, the system information sent bythe second terminal device, the method further comprises: receiving, bythe first terminal device, indication information sent by the secondterminal device, wherein the indication information is used to indicatethat the system information changes.
 6. The method according to claim 1,wherein the system information is system information required by thefirst terminal device, and the system information required by the firstterminal device is a part or all of system information delivered by anetwork device of a camped-on cell or a serving cell of the secondterminal device; and the system information required by the firstterminal device comprises: changed system information in the systeminformation required by the first terminal device or all systeminformation required by the first terminal device.
 7. An informationtransmission apparatus, comprising: a processing unit configured todetermine an on duration of the first terminal device, wherein the onduration of the first terminal device is a time in which the firstterminal device is configure to receive a message sent by the secondterminal device; and a receiving unit configured to receive, during theon duration of the first terminal device determined by the processingunit, system information sent by the second terminal device through asidelink between the first terminal device and the second terminaldevice without a need to maintain a cellular link.
 8. The apparatusaccording to claim 7, wherein the receipt, during the on duration of thefirst terminal device in the following manner, of the system informationsent by the second terminal device comprises: receiving, on a pagingoccasion of the first terminal device, the system information sent bythe second terminal device at least one time by using a resource in asending resource pool, wherein the sending resource pool is configuredor preconfigured by a network device by using a broadcast message; orreceiving, on a paging occasion of the first terminal device, the systeminformation sent by the second terminal device at least one time byusing a dedicated resource, wherein the dedicated resource is configuredby a network device for the second terminal device.
 9. The apparatusaccording to claim 8, wherein the system information is carried in aradio resource control (RRC) message that is sent by a network deviceand the RRC message is forwarded by the second terminal device.
 10. Theapparatus according to claim 7, wherein the receiving unit is furtherconfigured to: before receiving the system information sent by thesecond terminal device, receive indication information sent by thesecond terminal device, wherein the indication information is used toindicate that the system information changes.